Sodium blood test: normal range, low and high sodium explained

A sodium blood test measures the concentration of sodium in your blood. The body normally holds it within a narrow range, so a result outside that range says something about the balance between sodium and water: how much you take in, how much the kidneys pass out, and what is lost along the way. It is a routine part of an electrolyte or kidney panel.

What it measures

Sodium is an electrolyte, a mineral that carries an electrical charge in body fluids. Most of it sits in the fluid outside cells, where it helps keep blood pressure steady and lets nerves and muscles work. You take it in through food, mostly as table salt; the kidneys remove what you do not need in the urine, and a little is lost in sweat and stool.

The blood level reflects sodium relative to water. When water rises relative to sodium, the level falls and water moves into cells, making them swell. Brain cells are especially sensitive to this, which is behind many of the symptoms of low sodium.

Normal range

The usual range for blood sodium is 135 to 145 mmol/L, which is the same as 135 to 145 mEq/L. Some laboratories use slightly different limits, such as 136 to 144, so read your result against the range on your report.

Sodium (mmol/L)	Usually described as
Below 135	Low (hyponatraemia)
135 to 145	Usual range
Above 145	High (hypernatraemia)

What a low result usually points to

Low sodium, or hyponatraemia, is the most common disorder of body fluid and electrolyte balance seen in clinical practice. It usually points to one of these patterns:

• Too much water for the sodium present: heart failure, some kidney diseases, cirrhosis of the liver, or a condition called SIADH, in which the body holds on to water it would normally pass.
• Sodium lost with fluid: vomiting, diarrhoea, heavy sweating, burns, or water pills (diuretics).
• Hormones: an underactive thyroid, or adrenal glands that make too little of their hormones (Addison disease).
• Medicines: diuretics, some antidepressants (SSRIs), morphine, and some over-the-counter pain relievers.
• A reading effect: very high blood sugar or very high triglycerides can lower the measured sodium.

How fast sodium fell matters as well as how far: a drop that happens in under 48 hours is more dangerous than one that develops slowly, because the brain has less time to adjust. A doctor typically looks at symptoms, medicines and fluid intake, and may check blood and urine osmolality and urine sodium, along with glucose, and thyroid and adrenal function, since these are among the causes. Talk to a doctor about a low result, with the result in front of you.

What a high result usually points to

High sodium, or hypernatraemia, usually means the body has lost more water than sodium, or taken in too little water. Common reasons are not drinking enough, particularly in people who cannot easily reach fluids or sense thirst, heavy sweating, diarrhoea and burns. Less often it points to diabetes insipidus, in which the kidneys cannot conserve water, to adrenal conditions such as Cushing syndrome or hyperaldosteronism, to too much salt or sodium bicarbonate, or to medicines including corticosteroids, laxatives, lithium, ibuprofen and naproxen. A doctor usually reads it with the other electrolytes and kidney results before deciding what to look at next.

What moves it

• Fluids and salt. Unusually large or small amounts of fluid or salt, and intravenous fluids.
• Fluid losses. Sweating, vomiting and diarrhoea.
• Medicines. MedlinePlus lists some antibiotics, antidepressants, some blood pressure medicines, lithium, anti-inflammatory painkillers (NSAIDs) and water pills among those that can affect the test, and steroid hormones such as hydrocortisone.
• Recent illness, injury or surgery.
• Age, sex and other conditions, which can shift levels up or down.
• Glucose and triglycerides. Very high levels lower the measured result.

Preparing for the test

Sodium usually needs no special preparation, but it is often drawn with tests that need fasting, so follow the instructions for the whole panel. Drink water as you normally would. Tell the person taking the sample about any medicines, especially water pills, antidepressants and lithium, and do not stop a prescribed medicine for the test unless your doctor tells you to.

How Clare's panel handles it

In Clare's panel, sodium is measured by the lab, alongside potassium, chloride and bicarbonate. When Clare opens, members will see it next to those results and their own history, which is where a slow drift shows.

Price

Sodium is usually sold within a kidney function test rather than on its own. When we read public prices on 11 October 2026, a kidney function test cost from 89 to 900 at six UAE providers. Five of the six were 250 or less, and the top of the range was a specialised package. VAT was rarely stated, some figures were offer or "from" prices, and home collection can add a fee. Not every kidney package lists sodium, so check the contents.

Related tests

Sodium is read with potassium, chloride and bicarbonate, the other electrolytes measured with it; with fasting glucose, since very high sugar changes the reading; and with creatinine, since kidney disease is among the causes in both directions. For preparing for a full panel, see Comprehensive blood test in Dubai: what to expect.

Why the number means more over time

Because the body holds sodium within a narrow range, a value that has drifted steadily across several tests says something different from one low result after a day of heavy sweating or a lot of water. Doctors often check sodium in people taking medicines that affect fluid balance, such as diuretics, for the same reason: what matters is the direction and the speed, which one test cannot show.

Clare is opening with a waitlist at clare.health.